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#ifndef __SYMBOL_TABLE_H
#define __SYMBOL_TABLE_H
#include <map>
#include "types.hh"
namespace nix {
/* Symbol table used by the parser and evaluator to represent and look
up identifiers and attribute sets efficiently.
SymbolTable::create() converts a string into a symbol. Symbols
have the property that they can be compared efficiently (using a
pointer equality test), because the symbol table stores only one
copy of each string. */
class Symbol
{
private:
const string * s; // pointer into SymbolTable
Symbol(const string * s) : s(s) { };
friend class SymbolTable;
public:
bool operator == (const Symbol & s2) const
{
return s == s2.s;
}
bool operator != (const Symbol & s2) const
{
return s != s2.s;
}
bool operator < (const Symbol & s2) const
{
return s < s2.s;
}
operator const string & () const
{
return *s;
}
bool empty() const
{
return s->empty();
}
friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
};
inline std::ostream & operator << (std::ostream & str, const Symbol & sym)
{
str << *sym.s;
return str;
}
class SymbolTable
{
private:
typedef std::set<string> Symbols;
Symbols symbols;
public:
Symbol create(const string & s)
{
std::pair<Symbols::iterator, bool> res = symbols.insert(s);
return Symbol(&*res.first);
}
};
}
#endif /* !__SYMBOL_TABLE_H */
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